The present invention relates to a method and an apparatus for manufacturing polyethyleneterephthalate (PET) containers, such as bottles, which, during use, are capable of withstanding relatively severe heat conditions without undue deformation.
PET containers are widely used for the commercially for certain liquids containing gases such as CO.sub.2, for example carbonated lemonades, sodas, fruit juices, etc. However, due to their manufacturing process, these containers cannot be subjected, without undue deformation, to relatively severe heat conditions such as the high temperatures of up to 95.degree. C. encountered during the filling of the containers with a hot liquid or such as the fairly high temperatures (60.degree. to 80.degree. C.), which are maintained for a long period of time (1 to 2 hours), encountered during the pasteurization of the liquid contents of the containers. All these conditions are encountered during the packaging of certain flat liquids, such as non-carbonated fruit juices, or of certain carbonated liquids, such as beer.
Attempts have been made to overcome these disadvantages and to adapt PET containers for the stocking of products such as carbonated or non-carbonated fruit juices or beer. For this purpose PET bottles have ben produced which can withstand being filled with a hot liquid, about 85.degree. C., with relatively little deformation which is acceptable. Such filling gives the container a relatively brief thermal shock, on the order of a few minutes, and the relatively small deformation is limited solely by the brevity of the heat phenomenon.
Experience has shown, however, that these known containers cannot withstand the process of pasteurization of their liquid contents, which is generally conducted at a temperature below 85.degree. C.; this temperature varies as a function of the CO.sub.2 content, for example from 78.degree. C. for a liquid containing 3.5 g/liter of CO.sub.2 to 65.degree. C. for a liquid containing 6 g/liter of CO.sub.2. The treatment lasts about one hour, and the containers are unacceptably deformed by a variation in volume of 30% and more.